Pistons for cartridges for dispensing a multicomponent mixture are known, for example, from DE 200 10 417 U1, wherein the piston has a first piston part which is provided with a sealing lip that contacts the cartridge wall.
Another piston is disclosed in EP 1 165 400 B1 wherein the piston is made up of a soft plastic, for example LDPE (low density polyethylene) in order to achieve the required sealing effect toward the cartridge wall. However, such a piston may only be compatible with limitations with materials which form the filling of the cartridge. To avoid the piston coming into contact with such materials along its conveying side, a cover plate is used which is made of a plastic which is resistant to the filling. The cover plate covers a large part of the cross-sectional surface on the conveying side, with the exception of the marginal region which is adjacent to the cartridge wall. The marginal region is formed by a limb which extends outside the cover plate along the outer periphery of the piston in the direction of the conveying side. The limb is separated from the cover plate by a V-shaped groove. The limb in this embodiment is admittedly in contact with the filling, but the other regions of the piston are screened off by the cover plate. It applies to most fillings that a contact with the piston material results in a swelling of the piston material so that an expansion occurs in the region of the limb. This has the advantage that the sealing effect is in all events amplified. Alternatively to this, a plurality of sealing lips can also be arranged at the piston circumference, such as is known, for example, from CH 610 994.
However, these already known pistons have proved to be unsuitable for the discharge of fillings containing solids. Solids can enter into the intermediate space between the end of the limb and the sealing lip and remain captured in the intermediate space. If the discharge procedure is continued, the sealing lip sweeps over the solid grain contacting the cartridge wall. The contact of the sealing lip with the cartridge wall is lost, the sealing effect is accordingly no longer present.
A solution for this problem lies in providing a sealing lip which is located at the outermost end of the limb. However, such a sealing lip is not suitable for a practical application since the lip is easily damaged on the introduction of the piston into the cartridge. This problem can be remedied in that the piston itself is made deformable as, for example, the piston of CH 610 994.
However, the piston of CH 610 994 can only be used with an expulsion plunger of the piston adapted to the geometry of the piston when viscous or pasty media are to be discharged from a cartridge using this piston. This means this piston is not compatible with commercial discharge devices.
Accordingly, it is an object of the invention to provide an improvement to the named piston so that materials containing solids can be discharged using the piston, with the imperviousness of the piston remaining ensured.
It is another object of the invention to provide at piston that is displaceable in a cartridge by means of commercial discharge devices.
Briefly, the invention provides a piston for a cartridge that has a filling containing solid particles. The piston is displaceable in the cartridge to discharge the filling and has a scraper element which serves for the scraping of solid particles from the wall of the cartridge during discharge.
The piston includes a piston body having a conveying side, an oppositely disposed drive side and a piston jacket on the circumferential side forming a connection between the conveying side and the drive side. The piston jacket is arranged about a piston axis and merges on the conveying side into a projection which has a guide element for the guidance of the piston in the cartridge and for establishing a sealing contact with the wall of the cartridge. The conveying side is the side of the piston which is in contact with the filling while the drive side is the opposite side articulated to a drive mechanism, such as a plunger.
The projection includes a scraper element which has a surface that is at a smaller spacing from the conveying side than the guide element. The surface is usually part of a plane which is normal to the piston axis. The surface does not have to coincide with this plane, but can deviate from it if the piston has a curvature or has cut-outs and projections for the reception of stiffening elements, protective elements, venting elements and the like. A reference surface is assumed for the determination of the relative distance from the conveying element and the scraper element, said reference surface being in a plane which is spanned normal to the piston axis and contains the point or points of the piston which project the furthest into the filling. Or in other words: If the piston were placed with its conveyer side onto a planar surface and were aligned such that its piston axis is normal to this surface, this planar surface forms the reference surface. In accordance with this definition, the scraper element has a smaller distance from the reference surface than the guide element. Solids are hereby taken up by the scraper element during the discharge of the filling out of the cartridge and are expelled by the scraper element or are deflected in the direction of the piston axis so that the solid particles are completely discharged with the filling.
The scraper element has an edge which contains the points of the scraper element furthest away from the piston axis in the radial direction.
The guide element has a spacing from the piston axis in the radial direction which is larger than the spacing of the edge from the piston axis. This means that the guide element has a larger diameter than the edge. The guide element contacts the wall of a cartridge when the piston is located in the cartridge. The guide element can even have a diameter which is larger than the inner diameter of the cartridge, that is, the guide element can have an oversize with respect to the inner diameter of the cartridge. The sealing of the conveyer-side piston space from the drive side thus takes place by means of the guide element.
The edge of the scraper element has a radial spacing R1 from the piston axis and the guide element has a spacing R2 from the piston axis, with the difference amounting to a maximum of 0.5 mm, preferably 0.3 mm, particularly preferably 0.2 mm. Because the scraper element thus has a smaller radial extent than the guide element, the scraper element is not damaged on the assembly of the piston with the cartridge. As soon as the scraper element is introduced into the cartridge, the piston is centered by the scraper element and a tilting can be avoided. If the piston is moved further into the inner space of the cartridge, the guide element comes into contact with the wall of the cartridge at the circumferential side. Since, at best, small inclined positions of the piston are possible due to the centration of the scraper element, the contact pressure exerted by the wall onto the guide element will be distributed evenly over the periphery of the guide element. Damage of the guide element can hereby be avoided. The guide element can thus exert its sealing function as soon as the scraper element is in contact with the wall of the cartridge.
The edge of the scraper element bounds a support surface which is arranged between 80° and 110° relative to the piston axis and, in particular, substantially normal to the piston axis. A support surface of the scraper element thus adjoins the edge. This support surface proportionally takes up the compressive forces during the discharge of the filling which are exerted by the filling onto the piston when the filling should be discharged from the cartridge. The compressive forces acting on the support surface have a resultant force which extends in the direction of the piston axis. If the support surface is arranged at an angle of 80° to 110° to the piston axis, the compressive forces have the effect that the projection belonging to the scraper element is deformed such that the edge of the scraper element comes into contact with the wall of the cartridge.
In the projections known from the prior art, such as are shown in EP 1 165 400 B1, the projection has an inclined surface instead of an edge. The inclination thereof is designed such that the spacing between the projection and the cartridge wall increases in the direction of the conveying side. This inclined surface has the advantage that the piston can be introduced better into the cartridge. In particular when the projection has a diameter which is larger than the inner diameter of the associated cartridge, the piston can be positioned more easily in the bore of the cartridge. The end of the projection is in contact with the cartridge wall at the start of the assembly procedure of the piston in the cartridge. The further the cartridge is pushed into the bore, the further the contact line between the projection and the cartridge wall moves away from the end of the projection. At the same time, the projection undergoes an ever larger bias. The diameter of the projection increases more and more along the inclined surface. Since the inner diameter of the cartridge wall is, however, preset, the projection is deformed such that it can engage into the inner space of the cartridge. It also results from this that the projection is pressed toward the wall with an increasing contact pressure the further the assembly procedure progresses. This has the consequence that in the end position, when the piston has been pushed so far into the inner space of the cartridge that the sealing lip comes to lie at the inner wall, the end of the projection comes to lie at a spacing from the cartridge wall. The inclined surface remains present. When the piston is displaced by a discharge device, for example a plunger, for the discharge of the filling, the inner pressure of the filling exerts a force in the direction of the piston axis onto the inclined surface. This force can be divided into a force component directed normal to the inclined surface and into a force component directed in the direction of the inclined surface. It results from the force diagram that the force directed normal to the inclined surface attempts to move the projection away from the cartridge wall.
If a solid particle enters between the inclined surface and the cartridge wall, the solid particle supports this tendency. The solid particle is clamped, further and further into the gap between the inclined surface and the cartridge wall by the pressure of the filling. Since the piston and the sealing lip are made up of soft material, the piston material yields and the solid particle can pass the sealing lip. The contact between the sealing lip and the cartridge wall is hereby interrupted so that the solid particle and further filling material can emerge. This lack of seal is a problem which frequently occurs in the solutions of the prior art, in particular on the processing of fillings which contain solid particles.
The support surface advantageously has a section which includes an angle of up to 80°, preferably up to 60°, particularly preferably up to 45°, with the support surface. The angle can be determined as follows: a normal plane to the piston axis is laid by the edge of the support surface facing the piston axis. This normal plane is intersected by a plane which extends in the direction of the piston axis and which contains the edge, so that a line of intersection results. The angle is spanned between the line of intersection and the section line of the section with the plane extending in the direction of the piston axis.
The section is located on the side of the projection which is aligned to the piston axis, that is at the inner side of the projection. A compressive force which is caused by the filling likewise acts on the section. This force can in turn be divided into two force components, a normal component which is aligned normal to the section as well as a component which extends in the direction of the section. The section, and thus the projection including the edge, is pressed toward the wall of the cartridge by the normal component. The path for the solid particles is thus blocked; it is therefore possible to avoid solid particles coming to lie between the cartridge wall and the projection. It results from this that a deflection of any solid particles into the inner space of the piston takes place by means of the projection.
In another embodiment, the same advantage results for a ring-shaped piston. Such a ring-shaped piston additionally includes an inner piston jacket, with the inner piston jacket bounding the piston body at an inner side facing the piston axis, including an inner projection which includes an inner guide element for the guidance of the piston along the piston axis, with the inner guide element being suitable to establish a sealing contact with a wall of an inner tube. The inner projection includes an inner scraper element which has a smaller spacing from the conveying side than the guide element.
The ring-shaped piston also has as inner scraper element that includes an inner edge, with the inner edge containing the points of the inner scraper element least far away from the piston axis in the radial direction.
The inner guide element has a spacing from the piston axis in the radial direction which is smaller than or equal to the spacing of the inner edge from the piston axis.
The inner edge has a radial spacing R3 from the piston axis and the guide element has a radial spacing R4 from the piston axis, with the difference between R3 and R4 amounting to a maximum of 0.5 mm, preferably 0.3 mm, particularly preferably 0.2 mm.
The piston of either embodiment can be designed such that a protective element is attached to the piston body at the conveying side. Such a protective element can be made of a material which has a higher resistance with respect to the filling than the piston material. The protective element can thus develop a protective function for the piston material.
The piston body or the protective element can contain a venting element. This venting element serves to remove gases from gas inclusions from the inner piston space which arise, for example, on the insertion of the piston into the cartridge wall. The gas can in particular be air.
Stiffening ribs can be arranged on the drive side of the piston. The provision of stiffening ribs ensures that the piston remains inherently stable even if the piston is put under pressure by means of a discharge device on the discharge of the filling.
A tilt securing element can be arranged on the drive side of the piston and serves for the improvement of the guidance of the piston in a cartridge. The piston is guided securely against tilting by the tilt securing element which is in contact with the wall of the cartridge, thus the axis of the piston body coincides with the piston axis. The tilt securing element ensures that the conveying side is arranged in a normal plane to the piston axis or, if the conveying side is not planar, that points of the piston surface at the conveying side which are characterized by a specific radius and a specific height are disposed in substantially the same normal plane along the periphery. If the piston were to tilt, the condition for such points would not be satisfied. A contact with the wall of the cartridge at the circumferential side can be maintained during the whole discharge procedure by such a tilt securing element so that a deflection of the piston can be prevented together with the previously described guide element.
The advantages of the special features which the annular piston can have correspond to the advantages such as have been listed earlier in connection with a piston for a cylindrical inner space or an inner space of a different design without installations.
A discharge apparatus includes a piston in accordance with one of the preceding embodiments. The discharge apparatus includes a cartridge for the discharge of a plurality of components, with the components being arranged in cavities of the cartridge arranged next to one another or coaxially. Furthermore, the discharge apparatus can include a discharge device by means of which the piston can be connected at the drive side.
The piston in accordance with one of the preceding embodiments is particularly advantageously used for the discharge of fillings containing solids as well as pasty or viscous compounds.